
which is relevant to the background evolution and has been already fitted in the literature.
In particular, in Ref. [1]} it is found that \(s=0.254^{+0.118}_{-0.097}\)  with the CMB data by Planck, while it
shifted to \(s=0.16\pm {0.08}\)  when the RSD data is included.
For simplicity and illustrating our results, we fix the parameter of \(s\)  to be 0.25 by hand, and then
choose a simple set:
\(p_2&=1, \quad p=4; \quad s=0.25\,.\) 
